Pool vacumn and skimmer confusion

I have a 32,000 gal plaster pool. I have never really known how to use the vacumn. I know about the valve settings and the vacumn. What I don't understand are the skimmers. I read several post. I have two skimmers. There are two holes in each skimmer. Am I supposedto plug up the one furthest from the filter? Then which hole in the skimmer am I supposed to put the vacumn hose. Am I supposed to cover one of those holes. When the water in my pool gets low it does start sucking air. Appreciate any insight.